When driving a motor such as a DC motor and a stepping motor with high efficiency, a motor current is controlled by a pulse width modulation (PWM) control. In a motor drive system, it is important to detect a rotor position.
A voltage, a polarity and an inclination change with a wave height value and a phase delay amount of an induced voltage of a first phase and an induced voltage of a second phase, when the stepping motor detects an induced voltage in an interval where a motor control current does not flow, and detects a rotor position based on information of the voltage, the polarity, the inclination and the like. Therefore, there is a problem that it is difficult to detect the rotor position.